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Subject[RFC V3] test bit before clear files_struct bits
Test bit before clear close_on_exec and open_fds,
by trace __clear_bit(), these 2 place are false in most times,
we test it so that we don't need clear_bit, and we can win
in most time.
Add *_if_need bitop non-atomic version.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
fs/file.c | 9 +++++++--
include/asm-generic/bitops/non-atomic.h | 35 +++++++++++++++++++++++++++++++++
2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index ee738ea..2e08e6f 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -209,7 +209,7 @@ static inline void __set_close_on_exec(int fd, struct fdtable *fdt)

static inline void __clear_close_on_exec(int fd, struct fdtable *fdt)
{
- __clear_bit(fd, fdt->close_on_exec);
+ __clear_bit_if_need(fd, fdt->close_on_exec);
}

static inline void __set_open_fd(int fd, struct fdtable *fdt)
@@ -222,6 +222,11 @@ static inline void __clear_open_fd(int fd, struct fdtable *fdt)
__clear_bit(fd, fdt->open_fds);
}

+static inline void __clear_open_fd_if_need(int fd, struct fdtable *fdt)
+{
+ __clear_bit_if_need(fd, fdt->open_fds);
+}
+
static int count_open_files(struct fdtable *fdt)
{
int size = fdt->max_fds;
@@ -316,7 +321,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
* is partway through open(). So make sure that this
* fd is available to the new process.
*/
- __clear_open_fd(open_files - i, new_fdt);
+ __clear_open_fd_if_need(open_files - i, new_fdt);
}
rcu_assign_pointer(*new_fds++, f);
}
diff --git a/include/asm-generic/bitops/non-atomic.h b/include/asm-generic/bitops/non-atomic.h
index 697cc2b..0713e3b 100644
--- a/include/asm-generic/bitops/non-atomic.h
+++ b/include/asm-generic/bitops/non-atomic.h
@@ -105,4 +105,39 @@ static inline int test_bit(int nr, const volatile unsigned long *addr)
return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}

+/*
+ * __*_if_need version is used in cases that you don't want write a bit which
+ * have been set / clear, to avoid dirty cacheline.
+ */
+static inline void __set_bit_if_need(int nr, volatile unsigned long *addr)
+{
+ if (!test_bit(nr, addr))
+ __set_bit(nr, addr);
+}
+
+static inline void __clear_bit_if_need(int nr, volatile unsigned long *addr)
+{
+ if (test_bit(nr, addr))
+ __clear_bit(nr, addr);
+}
+
+static inline int __test_and_set_bit_if_need(int nr, volatile unsigned long *addr)
+{
+ if (!test_bit(nr, addr)) {
+ __set_bit(nr, addr);
+ return false;
+ } else {
+ return true;
+ }
+}
+
+static inline int __test_and_clear_bit_if_need(int nr, volatile unsigned long *addr)
+{
+ if (test_bit(nr, addr)) {
+ __clear_bit(nr, addr);
+ return true;
+ } else {
+ return false;
+ }
+}
#endif /* _ASM_GENERIC_BITOPS_NON_ATOMIC_H_ */
--
2.2.2

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